A Wind Turbine Generator (WTG) is used to convert kinetic energy comprised in the wind into another form of energy, such as mechanical energy and most often also from mechanical energy into electrical energy. A WTG as embodied herein is of a type with a rotational axis substantially in a direction of the wind. When assembled on site such WTG comprises a vertically extending tower with a base in a bottom of the tower and a nacelle which is supported by the tower on top of the tower. The nacelle can be rotated relative to the tower, such as in response to a direction of the wind and such as via a yawing system positioned in a transition between the tower and the nacelle.
During service of the WTG various items of the WTG may need replacement, such as due to wear and tear after several years of duty in the WTG. Furthermore, when servicing the WTG, service personnel may alternatively or additionally need various other items such as tools or other equipment. Such items may have a weight of several hundred kilos and thus may require help from a moving and/or a lifting device for moving and/or lowering and/or raising the items and/or tools and/or equipment from or to a position in an uppermost part of the WTG, such as to or from, respectively, the base of the tower.
Published European application EP2182202 discloses a method for removing and replacing an article of wind turbine equipment, such as a yaw drive, internal to a nacelle of a wind turbine tower without use of an external wind farm site crane or external rigging on the wind tower. The application discloses that external rigging of wind turbine tower components may expose workers and the equipment inside the nacelle to outside weather and hazardous wind conditions. The yaw drive is internally rigged with an internal support crane within the nacelle and translated to an internal winch capable of supporting the yaw drive during a lift to the base of the wind turbine tower.
The method includes a number of method steps and may, for example, be found to require a relatively high effort to perform a task which may be relatively simple, such as replacing a yaw drive in the yawing system. In consequence, embodiments of the present invention have been devised.